Glenn Reynolds at Instapundit recently linked to an article by Richard Martin in Wired Magazine entitled, ‘Uranium is so Last Century: Enter Thorium, the New Green Nuke.” I cringed when I read it. I suspect serious advocates of thorium did as well. It was a piece of scientific wowserism of a sort that has been the bane of nuclear power in the past, and that its advocates would do well to steer clear of in the future. It evoked a romantic world of thorium “revolutionaries” doing battle with the dinosaurs of conventional nuclear power. Things aren’t quite that black and white in the real world. Thorium breeders deserve fair consideration, not hype, as does nuclear power in general. There are many good reasons to prefer it to its alternatives as a source of energy. It doesn’t take a genius to understand those reasons, assuming one approaches the subject with a mind that isn’t made up in advance, and is willing to devote a reasonable amount of time to acquire a basic understanding of the technology. Martin would be well advised to do so before writing his next article on the subject.
In the first place, thorium is not a replacement for uranium, as implied by the title of the Wired article. Rather, the point of putting it in nuclear reactors is to breed uranium, which remains the actual fuel material, albeit in the form of isotope U233 rather than U235. Thus, when Martin writes things like,
Those technologies are still based on uranium, however, and will be beset by the same problems that have dogged the nuclear industry since the 1960s. It is only thorium… that can move the country toward a new era of safe, clean, affordable energy.
in comparing thorium reactors to their more conventional alternatives, it is evident he doesn’t know what he is talking about. Referring to the physicist Alvin Weinberg, he tells us,
Weinberg and his men proved the efficacy of thorium reactors in hundreds of tests at Oak Ridge from the ’50s through the early ’70s. But thorium hit a dead end. Locked in a struggle with a nuclear- armed Soviet Union, the US government in the ’60s chose to build uranium-fueled reactors — in part because they produce plutonium that can be refined into weapons-grade material. The course of the nuclear industry was set for the next four decades, and thorium power became one of the great what-if technologies of the 20th century.
With all due respect to Weinberg, a brilliant scientist whose work remains as relevant to conventional reactors as to their thorium cousins, this picture of thorium knights in shining armor doing battle with the dark forces of the nuclear weapons establishment is certainly romantic, but it leaves out some rather salient facts. In the first place, conventional power reactors do not even produce weapons grade plutonium, which contains a high concentration of plutonium 239. Special reactors that run for a much shorter period of time are used for that purpose. Furthermore, thorium is not a nuclear fuel. A reactor using thorium alone would never work because thorium is not a fissile material. In other words, unlike, for example, uranium 235 or plutonium 239, it cannot sustain a nuclear chain reaction. The point of putting it in nuclear reactors is to breed uranium 233, another isotope that is fissile. We began producing nuclear power with conventional nuclear reactors based on uranium 235 rather than thorium breeders because of their simplicity, not because of their usefulness as sources of bomb material. The fuel needed to run them is available in nature as one of the isotopes in mined uranium, and doesn’t depend on a complex breeding cycle for its production. There are other drawbacks to thorium breeders that Martin doesn’t mention in his article. For example, in addition to uranium 233, they produce significant quantities of uranium 232, a short lived isotope with some nasty, highly radioactive daughters. Separating it from U233 was out of the question, and its presence makes the production and handling of nuclear fuel elements a great deal more difficult.
I’m certainly no opponent of thorium breeders. In fact, I think we should be aggressively developing the technology. However, before writing articles about the subject, it can’t hurt to have some idea what you’re talking about. There are no lack of good articles about the subject on the Web within easy reach of anyone who can use Google.